As a disk recording medium device in which a disk-like recording medium capable of recording and/or reproducing information such as audio data, video data or computer data is accommodated within a cartridge housing so as to become freely rotatable, there is known a disk recording medium device having an arrangement shown in FIG. 32, for example. This disk recording medium device 1 is an information recording media which incorporates therein a write once magneto-optical disk 4 on which users are able to record (write) information such as computer data later on.
This disk recording medium device 1 comprises a cartridge housing 2 composed of a pair of upper shell 2a and lower shell 2b, the magneto-optical disk 4 accommodated within a disk compartment 3 of this cartridge housing 2 so as to become freely rotatable and so forth. The cartridge housing 2 has on its upper and lower surfaces provided an upper and lower opening portion 5 that extends from a central portion to one side. This opening portion 5 can be opened and closed by a shutter member 6 that can slide along one side. The shutter member 6 is constantly spring-biased in the direction to close the opening portion 5 under spring force of a spring, not shown. Reference numeral 6a denotes a presser member for preventing a tip end portion of the shutter member 6 from being disengaged from the opening portion inadvertently.
The magneto-optical disk 4 has at its central portion provided a disk-like center hub 7 made of metal. This center hub 7 is located at the position opposing to the inner end portion of the opening portion 5, i.e. located at substantially the central portion of the cartridge housing 2. A turntable provided on the main body side of an information recording and reproducing apparatus is mounted to the center hub 7. The magneto-optical disk 4 is chucked to and fixed to the turntable and thereby the magneto-optical disk is rotated at predetermined velocity (e.g. constant linear velocity). At that time, a magneto-optical pickup device of which the head portion is inserted into the opening portion 5 functions to record or reproduce an information signal on or from the magneto-optical disk 4.
However, in the conventional disk recording medium device having the above-mentioned arrangement, a shutter member 6 for opening and closing an opening portion 5 is slidably engaged with one side of the cartridge housing 2 and this shutter member 6 is spring-biased in one direction under spring force of a spring to close the opening portion 5. On the other hand, the shutter member 6 is moved against spring force of this spring to open the opening portion 5. Therefore, since the surface in which the cartridge housing 2 and the shutter member 6 are overlapping with each other is formed of the flat surface, there arises a problem in which dusts may enter into the disk compartment from such clearance relatively easily from the outside.
In view of the aforesaid problems and the like encountered with the prior art, since the portion in which the shutter member and the cartridge housing are overlapping with each other is formed of the flat surface and the dusts and smudges may enter into the disk compartment relatively easily from the clearance of that portion, it is an object of the present invention to provide a disk cartridge, a disk recording medium device and a disk recording and/or reproducing apparatus which are excellent in dust-proof performance and in which a dust-proof clearance that is concaved and convexed in the thickness direction is provided by forming corresponding convex rib and concave groove on the overlapping portion, the labyrinth-like dust-proof clearance can suppress small dusts and smudges from passing and in which dusts and smudges can be made difficult to enter into the disk compartment.